Electrically actuated trailer brake control system

ABSTRACT

Upon applying the brakes of a pulling vehicle, an electrical signal is used to actuate the trailer brakes. After applying the brakes of the pulling vehicle and the trailer, an electrical control system is used to control the trailer brakes hydraulic pressure as a function of the pulling vehicle&#39;&#39;s brake line pressure. As a pressure differential is detected between the pulling vehicle and the trailer, the electrical system decreases the trailer brake pressure until the differential no longer exists. The intelligence used to control the trailer brake hydraulic pressure is obtained from a pressure transducer in the brake line of the pulling vehicle, from a pressure transducer in the brake line of the trailer, and from the brake switch of the pulling vehicle. By inclusion of a proper feedback in the electrical control system, the pressure in the brake line of the trailer will not be changed by minor variations.

United States Patent [1 1 Howard ELECTRICALLY ACTUATED TRAILER BRAKECONTROL SYSTEM [76] Inventor: Donald W. Howard, 401 N. Bendix Dr., SouthBend, Ind. 46620 [22] Filed: Mar. 15, 1972 [21] Appl. No.2 234,746

[52] U.S. Cl 303/7, 188/3 R, 303/20, 395M- [51] Int. Cl B60t 13/68 [58]Field of Search 188/3 R [56] References Cited UNITED STATES PATENTS3,659,903 5/1972 Sarbach 303/20 3,402,972 9/1968 Cooper et al.... 303/203,507,542 4/1970 Cannella 188/3 R X 3,656,817 4/1972 Okamoto et al.303/20 X 3,350,142 10/1967 Schuman 303/20 X 3,574,414 4/1971 Jacob 188/3R X I Primary Examiner-Milton Buchler Assistant ExaminerStephen G. KuninAttorn'ey-Ken C. Decker et al.

[5 7 ABSTRACT draulic pressure is obtained from a pressure transducer inthe brake line of the pulling vehicle, from a pressure transducer in thebrake line of the trailer, and from the brake switch of the pullingvehicle. By inclusion of a proper feedback in the electrical controlsystem, the pressure in the brake line of the trailer will not bechanged by minor variations.

5 Claims, 2 Drawin Fi COMPARATOR TRANSISTOR Z0 SWITCH- 32 SWIT CHSOLENOID ENGINE VACUUM ATMOSPHERE Patented Oct. 30, 1973 COMPARATORSWITCH TRANSISTOR ATMOSPHERE BRAKE SWITCH SOLENOI ELECTRICALLY ACTUATEDTRAILER BRAKE CONTROL SYSTEM BACKGROUND OF THE INVENTION This inventionrelates to a trailer brake control system. More particularly, theinvention is directed to an electrically actuated trailer brake controlsystem. The source of power for the trailer brake control system may beeither a vacuum line from the pulling vehicle, an electric pump operatedfrom the pulling vehicles battery, or even a mechanical pump driven fromthe turning of the trailer wheels.

Previous to the present invention, there has been a problem withdifferences in brake torque developing between the trailer and thepulling vehicle. Unless the proper brake pressure is applied both to thepulling vehicle and to the trailer, problems can result. If the trailerbrake pressure is too great, then the trailer will tend to drag thepulling vehicle to a stop upon applicationof the brakes. However, if thevehicle brake pressure is too great, the trailer will tend to run overthe pulling vehicle while being braked to a stop.

Prior to the present invention, many trailers did not have any type ofbraking system whatsoever, especially among recreational vehicles. Manyof these trailers depend entirely upon the braking ability of thepulling vehicle to stop both the pulling vehicle and the trailer. Othersystems have been developed whereby brake line pressure from the pullingvehicle is fed back to the trailer. Still another system that is in morecommon usage is for a vacuum from the engine of the pulling vehicle tobe fed back to the recreation type trailer. This vacuum pressure may beused to actuate .a hydraulic braking system. Yet another popular systemis the type which provides electrically actuated brakes on the trailer.These systems are actuated by the towing vehicles electrical system whena brake actuation is effected. In recreational trailers the amount ofmoney that can be spent on a braking system is much less than for thetractor-trailer vehicles. Therefore, any braking system must be aseconomical as possible and as reliable as possible to meet the budgetsof the average owner.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto provide an electrically actuated vacuum powered, trailer brakecontrol system.

It is a further object of the present invention to provide proportionalbrake pressure between the pulling vehicle and the trailer.

A still further object of this invention is toprovide brake pressure forthe trailer that can be varied according to the load of the trailer toprovide a uniform braking force from the pulling vehicle and the trailerupon application of the vehicle brakes.

It is an even further object of the present invention to provide a solidstate electrical control system for regulating the brake pressure of thetrailer. The solid state electrical control system will have a feedbacknetwork to prevent responses to insignificant changes in brake pressure.

These and other objects are accomplished in the present invention inwhich pressure transducers monitor the brake line pressure of thepulling vehicle and the trailer. A comparison of the brake line pressure.of the pulling vehicle and the trailer through a comparator network cangive an output proportional to any given difference in brake pressure.This output can be used to regulate the brake pressure in the trailer.By regulat- BRIEF DESCRIPTION OF THE DRAWINGS The invention hereindisclosed will be more fully understood when taken together with theaccompanying drawings in which:

FIG. 1 is a functional diagram that shows the electrical control systemand how it is used to control the power boost in a hydraulic brakesystem, the power boost being shown in a cross sectional view;

FIG. 2 is a detailed electrical schematic of the electrical controlsshown in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With continued reference to theaccompanying figures, and with initial attention directed to FIG. 1,reference numeral 10 generally designates the electronic controls of thefunctional block diagram. A general presentation will be given firstwith more details given on the electronic controls 10 thereafter.

Transducers l2 and 14 are used to monitor the brake line pressure of thepulling vehicle and the trailer respectively. The transducers l2 and 14are illustrated functionally as variable resistors. After turning on theignition switch which closes contacts 16, essentially no current flowsfrom the +12 volts to ground because the transducers 12 and 14 are of avery high resistance. Upon applying the brakes of the pulling vehicle,transducer 12 changes to a lower resistance, which allows current toflow through resistor 18. The current flowing through resistor 18develops a voltage which is fed into comparator 20. Upon application ofthe brakes of .the pulling vehicle, the brakeswitch closes whichautomatically energizes solenoid 22. The energization of solenoid 22closes normally open valve 24';

The power booster 26 is vacuum operated from the engine vacuum. Beforethe closing of normally open valve 24, power booster 26 contains adiaphragm 28 that is suspended in a vacuum system. Before theapplication of the vehicle brakes, a normally closed valve 30 preventsatmospheric pressure from reaching the back side of diaphragm 28. Uponapplying the brakes of the pulling vehicle and the development ofvoltage across resistor 18, a voltage is fed into comparator 20. Sincetransducer 14 is still at a high resistance value, very little voltageis developed across resistor 32. Since little current is flowing throughresistor 32 and no voltage is being fed into comparator 20 fromtransducer 14, comparator 20 will give a voltage output which issubsequently fed into transistor switch 34. Transistor switch 34 is usedto amplify the output of comparator 20 and energize solenoid 36. Theenergization of solenoid 36 will open normally closed valve 30. The timelag between the closing of normally open solenoid valve 24 and theopening of normally closed valve 30 is infinitesimal and will haveessentially no result on the brake line pressure of the trailer.

The opening of normally closed valve 30 will allow pressure to developon the back side of diaphragm 28. Since normally open valve 24 hasisolated the back side of diaphragm 28 from the engine vacuum, theatmospheric pressure inside of power booster 26 will force diaphragm 28and the power plunger 38 forward into the master cylinder 40. The mastercylinder 40 may be either a single or a dual master cylinder or anyother standard type. As a result of the force applied by the powerplunger 38, the master cylinder 40 will put a pressure on the fluid inbrake lines 42. The pressure in brake lines 42 will operate the brakecylinders 44 and 46 to apply the brakes 48 and 50. The transducer 52represents the hydraulic connection of transducer 14.

Referring more specifically to the power booster 26, the diaphragm 28has a slow bleed 54. Therefore, after the voltage developed acrossresistor 32 reaches essentially the same voltage as developed acrossresistor 18, both of which are fed into comparator 20, no output signalwill result therefrom. Hence, the output of transistor switch 34 willdrop to essentially zero thereby deenergizing solenoid 36 and closingnormally closed valve 30. While both normally closed valve 30 andnormally open valve 24 are closed, the slow bleed 54 allows a gradualreduction in atmospheric pressure on the back side of diaphragm 28.Hence, when the brake line pressure of the trailer falls below the brakeline pressure of the pulling vehicle, comparator 20 will again have anoutput and transistor switch 34 will again energize solenoid 36. Thiswill again allow the opening of normally closed valve 30 and againincrease the fluid pressure applied through master cylinder 40 and brakelines 42 to the brake cylinders 44 and 46. By proper selection of theslow bleed 54 and the size of the booster 28, the cyclic rate ofnormally closed valve 30 can be kept very low. When the trailer brakepressure falls slightly below the brake pressure of the pulling vehicle,the normally closed valve 30 can be pulsed open for a short period oftime and the brake pressure of the trailer will be increased at whichtime the normally closed valve 30 will again be deenergized.

Referring now to FIG. 2 which shows the electronic controls of FIG. 1,like numerals will be used to designate the same parts. Prior to thebrake application, both the emitter and collector of transistor 56 areat ground potential because essentially no current is flowing throughresistor 18 because of the large resistance value of transducer 12. Thesolenoid 22 which is used to operate the normally open valve 24 is alsodeenergized because the brake switch 58 is open. Upon application of thevehicle brakes, the brake switch 58 is closed and the solenoid 22 isenergized, thereby closing normally open valve 24. Because essentiallyno voltage is being developed across resistor 32, solenoid 36 will beenergized, thereby opening normally closed valve 30. This is broughtabout by the electronic controls as shown in more detail in FIG. 2.

The transistor 56 is turned on upon application of the vehicle brakesbecause the emitter voltage developed across resistor 18 is higher thanthe voltage developed across resistor 32 and connected to the base oftransistor 56. The conduction of transistor 56 will develop a voltageacross resistor 60, thereby causing the conduction of transistor 62.Transistor 62 which is a level detector will cause a current to flowthrough resistor 64 when conducting. The voltage developed acrossresistor 64 will cause the first stage of the transistor switch 34,which is transistor 66, to conduct. The conduction of transistor 66 willfeed a current through resistor 68 into the base of transistor 70,thereby causing transistor 70 to conduct. The conduction of transistor70 will cause current to flow through solenoid 36, and thereby, opennormally closed valve 30. Resistor 72 is a normal bias resistor. Diode74 and its series resistor 76 act as a damping network to protect thepower transistor 70 when solenoid 36 is turned off.

As the brake pressure of the trailer increases and approaches the brakepressure of the pulling vehicle, the base voltage of transistor 56approaches the emitter voltage. When these voltages are nearly equal,the comparator 20 and the subsequent transistor switch 34 are turnedoff, thereby deenergizing the solenoid 36 which prevents any furtherincrease in pressure on the back side of diaphragm 28. The slow bleed 54then allows the brake pressure of the trailer to slowly decay. Byincorporation of a dead band within the control unit, which can be doneby a large resistor 78, the range of slow pressure decay can be adjustedto provide a smooth control of brake pressure in the trailer in responseto the brake pressure of the pulling vehicle.

As a further feature of the present invention, only three wires need beconnected from the pulling vehicle to the trailer. Connectors 80, 82,and 84 represent the pin connections of these three wires that may beincorporated into a single cable connector. Furthermore, since theentire electronic controls 10, except for transducers l2 and 14, may bemade from a single integrated circuit, the entire integrated circuit maybe contained within the connector itself. Therefore, connectors 86, 88,and may be pin connections within the cable connection and feed signalsdirectly into an integrated circuit portion of the electronic controls10. All of the integrated circuit could be contained within the cableconnector.

By the inclusion of integrated circuits within the electronic controlsof the present system, the cost of producing the present braking systemmay be kept to a minimum. This would make the present braking systemvery attractive for recreational type vehicles, especially campertrailers to be pulled behind normal familyowned vehicles. The onlyconnections necessary between the pulling vehicle and the trailer wouldbe a three-wire connector that anyone could very easily connect. If thepower booster 26 is vacuum operated, then the only additional connectionnecessary would be to connect the engine vacuum from the pulling vehicleto the power booster 26. However, it is possible for the trailer brakesystem to have its own source of power or to be operated from a +12 voltpump driven by the battery of the pulling vehicle. Also, it is possiblethat the trailer may have a mechanical pump driven by the rotation ofthe wheels of the trailer. Whatever the source of power for theoperation of the brakes of the trailer, it would take a minimum of costto have the electrically actuated trailer brake control system as shownin the present invention. There is a tremendous need, especially in therecreational vehicles, for an economic system that will keep the brakepressure in the trailer proportional to the brake pressure in thepulling vehicle. Mechanical adjustments should be included in thetransducers 12 and 14 to allow for differences in brake pressure ofpulling vehicles and loads within the trailer. These mechanicaladjustments could allow any trailer with any type of weight to be pulledby any vehicle that could pull the load, and still get a smooth, uniformstop. Both the trailer and the pulling vehicle would apply theirproportionate share to the braking force.

I claim:

1. A means for controlling brake pressure of a towed vehicle as afunction of brake pressure of a towing vehicle, said controlling meanscomprising:

a first means for monitoring brake pressure in said towing vehicle;

a second means for monitoring brake pressure in said towed vehicle;

means for comparing outputs from said first monitoring means and saidsecond mointoring means, said comparing means having an outputproportional to any difference between the brake pressures of saidtowing vehicle and said towed vehicle;

power means for applying the brakes of said towed vehicle when thebrakes of said towing vehicle have been applied; and means for varyingsaid power means as a function of said proportional output of saidcomparing means, said varying means keeping brake pressure in said towedvehicle proportional to brake pressure in said towing vehicle, I

said varying means comprising a switching means for operating a valvingmeans from said proportional output, said valving means reducing forcefrom said power means to the brakes of said towed vehicle,

said valving means providing a fast reduction in force from said powermeans, said power means comprising a means for slowly reducing the forcefrom said power means to the brakes of said towed vehicle.

2. In a brake actuation system for actuating the brakes of a trailer inresponse to a brake actuation of the towing vehicle:

means for generating a first signal proportional to the braking pressuregenerated by the towing vehicle;

means for generating a second signal proportional to the brakingpressure generated in the trailer;

means for comparing said first and second signals and generating a thirdsignal when the first signal exceeds the second signal by apredetermined amount,

means for generating a fourth signal when the brakes of the towingvehicle are actuated,

means for generating braking pressure in said trailer including ahousing, a diaphragm in said housing, means responsive to movement ofsaid diaphragm for generating said trailer braking pressure, saiddiaphragm defining a pair of chambers between opposite sides of thediaphragm and corresponding ends of said housing, means normallycommunicating each of said chambers to a common pressure source, meansresponsive to said fourth signal for terminating communication betweenone of said chambers and said common pressure source, and meansresponsive to said third signal for initiating communication betweensaid one chamber and another pressure source greater than the commonpressure source whereby said diaphragm means is moved to generatetrailer braking pressure.

3. The invention of claim 2,

said common pressure source being the engine manifold vacuum of thetowing vehicle, said another pressure source being atmospheric pressure.

4. The invention of claim 3, and

a bleed orifice in said diaphragm to permit limited communicationbetween said chambers, and resilient means yieldably urging saiddiaphragm means toward said one chamber, whereby said trailer brakingpressure is gradually reduced during generation of said fourth signalwhen said third signal is not generated.

5. The invention of claim 3; and

means within said braking pressure generator means to gradually reducetrailer braking pressure during generation of said fourth signal whensaid third signal is not generated.

1. A means for controlling brake pressure of a towed vehicle as afunction of brake pressure of a towing vehicle, said controlling meanscomprising: a first means for monitoring brake pressure in said towingvehicle; a second means for monitoring brake pressure in said towedvehicle; means for compariNg outputs from said first monitoring meansand said second monitoring means, said comparing means having an outputproportional to any difference between the brake pressures of saidtowing vehicle and said towed vehicle; power means for applying thebrakes of said towed vehicle when the brakes of said towing vehicle havebeen applied; and means for varying said power means as a function ofsaid proportional output of said comparing means, said varying meanskeeping brake pressure in said towed vehicle proportional to brakepressure in said towing vehicle, said varying means comprising aswitching means for operating a valving means from said proportionaloutput, said valving means reducing force from said power means to thebrakes of said towed vehicle, said valving means providing a fastreduction in force from said power means, said power means comprising ameans for slowly reducing the force from said power means to the brakesof said towed vehicle.
 2. In a brake actuation system for actuating thebrakes of a trailer in response to a brake actuation of the towingvehicle: means for generating a first signal proportional to the brakingpressure generated by the towing vehicle; means for generating a secondsignal proportional to the braking pressure generated in the trailer;means for comparing said first and second signals and generating a thirdsignal when the first signal exceeds the second signal by apredetermined amount, means for generating a fourth signal when thebrakes of the towing vehicle are actuated, means for generating brakingpressure in said trailer including a housing, a diaphragm in saidhousing, means responsive to movement of said diaphragm for generatingsaid trailer braking pressure, said diaphragm defining a pair ofchambers between opposite sides of the diaphragm and corresponding endsof said housing, means normally communicating each of said chambers to acommon pressure source, means responsive to said fourth signal forterminating communication between one of said chambers and said commonpressure source, and means responsive to said third signal forinitiating communication between said one chamber and another pressuresource greater than the common pressure source whereby said diaphragmmeans is moved to generate trailer braking pressure.
 3. The invention ofclaim 2, said common pressure source being the engine manifold vacuum ofthe towing vehicle, said another pressure source being atmosphericpressure.
 4. The invention of claim 3, and a bleed orifice in saiddiaphragm to permit limited communication between said chambers, andresilient means yieldably urging said diaphragm means toward said onechamber, whereby said trailer braking pressure is gradually reducedduring generation of said fourth signal when said third signal is notgenerated.
 5. The invention of claim 3; and means within said brakingpressure generator means to gradually reduce trailer braking pressureduring generation of said fourth signal when said third signal is notgenerated.